earthlike gliese 581 e, smallest exoplanet, water world, discovery, planet
earthlike, gliese 581 e, gliese 581 d, water world, candidate
gliese 581, water world candidate, gliese 581 d, earth-like habitable goldilocks zone

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Earthlike exoplanets
Gliese 581 d - a water world candidate
Gliese 581 e - lightest smallest so far

exoplanet Gliese 581 d
This artists conception shows planets orbiting the red dwarf star Gliese 581 with the newly
discovered planet, Gliese 581 e, in the left foreground and Gliese 581 d at a distance.

On Tuesday 21 April 2009 details were released, during the European Week of Astronomy and Space Science then being held at the University of Hertfordshire (and in a paper submitted to the journal Astronomy and Astrophysics), of Gliese 581 e, which, at 1.9 times the size of the earth in terms of mass is the lightest exoplanet to be fully recognised as being discovered so far.

By April 2007 some 227 exoplanets had been discovered by various astronomers and by April 2009 some 350 such exoplanets were known of.
Almost all exoplanets discovered to date have been large gas giants each with several times the mass of the Earth.

Although the Gliese system is all of 20.5 light-years, (that is 118,000,000,000,000 miles), from Earth, nevertheless in astronomical terms Gliese 581, a "Red Dwarf" star in the constellation Libra, is one of our near neighbours being the 87th closest known star system to our own Sun.

In April 2007 astronomers working with the European Southern Observatory in La Silla in the Chilean Andes made public their discovery of three exoplanets Gliese 581 b, Gliese 581 c and Gliese 581 d, orbiting Gliese 581, (the "a" identifier being reserved to avoid confusion with the star itself), and estimated these three exoplanets as being of fifteen to seventeen earth masses in the case of "b", five earth masses in the case of "c", and with Gliese 581 d being of some seven earth masses.

The same team have now discovered the existence of another exoplanet in the "Red Dwarf" star Gliese 581 system, Gliese 581 e, and the availability of more data has enabled them to place Gliese 581 d in a so called habitable zone, or goldilocks zone, where climatic conditions are neither too hot nor too cold and with the added possibility of Gliese 581 d also being a serious water world candidate as it appears to complete its entire orbit, which is estimated at taking 66.8 days, at a distance from this relatively cool star which locates the planet within a zone where water could remain liquid!
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exoplanet Gliese 581 d

This diagram depicts the distances of the planets in our own Solar System (upper row),
and in the Gliese 581 system (lower row), from their respective stars (left)
where 1 AU = the average distance between the Earth and the Sun.
The potentially habitable zone is indicated as the light blue area, showing that Gliese 581 d
is located largely inside the habitable zone around its cooler, low-mass, red star.
Based on a diagram by Franck Selsis, Univ. of Bordeaux. Credit: ESO

Gliese 581 "d" and "e" are regarded as being the two known exoplanets that have the most potential to be Earth-like. Gliese 581 e for its size, it ranks as the lightest exoplanet yet documented, and Gliese 581 d is seen as being earthlike because it may be the first serious water world candidate amongst the known exoplanets.

With the discovery of Gliese 581 e - which lies only some three million miles its Red Dwarf sun - although it would be scaldingly hot and completes its orbit in only 3.15 days (both of these being serious obstacles to habitability) - astronomers have nevertheless more cause than previously to believe that natural forces may have given rise to the existence of smaller planets in large numbers - possibly in their billions - across the Universe.

"The Holy Grail of current exoplanet research is the detection of a rocky, Earth-like planet in the 'habitable zone'," Michel Mayor, an astrophysicist at Geneva University in Switzerland, said in a statement.

And speaking of Gliese 581 d at the meeting in Hertfordshire Dr. Mayor said:-

"It lies in the [life-supporting] habitable zone, and it could have an ocean at its surface."

"We can only speculate at this stage, but it may have a rocky core, encased in an icy layer, with a liquid ocean at the surface and an atmosphere."

Dr. Mayor’s group also discovered the first exoplanet (called 51 Pegasi b), a gas giant 160 times the mass of the Earth, in 1995, using a technique known popularly as the “wiggle” method that detects planets by a slight gravitational tug they give their stars. The method is most sensitive to massive planets in close orbits. In a statement, Dr. Mayor noted that Gliese 581 e is only one-eightieth of the mass of 51 Pegasi b, saying,

“This is tremendous progress in 14 years.” - "It is amazing to see how far we have come since then."

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Earth-like exoplanets
Gliese 581 d - a water world candidate
Gliese 581 e - lightest smallest so far